In order to facilitate reference to various journal articles in the discussion of various aspects of this invention, a complete listing of the reference is provided at the end of the disclosure. Otherwise the references are identified in the disclosure by first author's name and publication year of the reference.
The childhood spinal muscular atrophies (SMAs) are a group of autosomal recessive, neurodegenerative disorders classified into three types based upon the age of onset and clinical progression (Dubowitz et al., 1978; Dubowitz et al., 1991). All three types are characterized by the degeneration of the alpha motor neurons of the spinal cord manifesting as weakness and wasting of the proximal voluntary muscles. Type I SMA is the most severe form with onset either in utero or within the first few months of life. Affected children are unable to sit unsupported and are prone to recurrent chest infections due to respiratory insufficiency, thus rarely surviving the first few years of life (Dubowitz et al., 1978; Dubowitz et al., 1991). This acute form, with a carrier frequency of 1/60 to 1/80, is one of the most frequent fatal autosomal recessive disorders. Affected children with Type II SMA never walk unaided and although the prognosis is variable, such children may die in adolescence. Those affected with Type III SMA maintain independent ambulation but develop weakness any time between the age of 3 to 17 years manifesting a mildly progressive course (Dubowitz et al., 1978; Dubowitz et al., 1991).
In 1990, all three childhood forms of SMA were genetically mapped to the long arm of chromosome 5 at 5q11.2-13.3 (Brustowitcz et al., 1990; Gilliam el al., 1990; Melki el al., 1990). Subsequent multi-point linkage analyses and the identification of recombinant events have further localized the genetic defect to the region flanked centromerically by D5S435/D5S629 (Soares et al., 1993; Wirth et al., 1993, Clermont et al., 1994)) and telomerically by MAP1B/D5S112 (Wirth et al., 1994; MacKenzie et al., 1993; Lien et al., 1991). This interval has been refined by the more recent identification of recombination events indicating that the SMA gene lies distal to CMS-1 (Yaraghi et al., submitted to Human Genetics; van der Steege, et al., submitted to Human Genetics) and proximal to D5S557 (Francis et al., 1993). We and others have detected chromosome 5-specific repetitive sequences with particular abundance in the D5S629/CMS-D5S557 region (Francis et al., 1993; Thompson et al., 1993) which has impeded the isolation and ordering of both clones and simple tandem repeats. An array of cosmid clones spanning the 200 kb CMS-1 (Kleyn et al., 1993)/CATT-1 (Burghes et al., 1994, McLean et al., in press)/D5F150/D5F149/D5F153 (Melki et al., 1994) region within this interval has been constructed.
We established a contiguous array of YAC clones encompassing the SMA containing D5S435-D5S112 interval of 5q13.1. We then discovered a gene within this interval of 5q13.1 which coded for a neuronal apoptosis inhibitor protein (NAIP). Further studies demonstrated that a deletion in this gene was found in Type I, II and III Spinal Muscular Atrophy.